Core Material In Casting

What Is Core Material For Casting?

A green sand core and a dry sand core are made of sand and binders. These core materials are used for making sand cores to be used in the sand molding process.

Core making takes place in a foundry using core boxes.

I have explained below the sand and binders used for making core in casting process.

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Following core sand is used for making core.

Sand For Making Core (Core Sand)

Core sand used for making core is as follows:

Silica sand.
Zircon sand.
Chromite Sand.
Carbon sand.
Olivine sand.

Silica sand, zircon sand and chromite sand are base sand used for making cores.

Sand having more than 5% clay cannot be used for making cores.

More than 5% clay content in core sand reduces permeability and collapsibility.

For core sand size, shape and distribution of the grain are important for making smooth holes and recesses.

A round grain shape with low clay content creates a smooth surface finish to the hollow casting.

Angular grains reduce permeability and decrease the surface finish of the casting.

The type of sand used depends upon the molten metal and the pouring temperature of the molten metal.

Sand used for making cores is almost pure sand without any natural bond.

Core Binders

Bonding agents need to be added to make the sand core.

The more commonly used binding agent for making the core is clay and cereals.

Binders need to be hardened at room temperature, during baking and bind the sand together to make a strong core

The binding agents used for making sand core are as follows:

Core oils.
Thermosetting binders.
Dextrine.
Resin.
Sulphiteliquior.
Proline.
Molasses.
Cereals.

Core Oil As Binder

(Binding agent used with sand for making core)

Core oils are the best economical option for making cores. Oils used as a binding agents are vegetable oil, corn oil, and linseed oil.

When used with core sand, oils are called oil sand.

Oil sand has the following advantages for core making:

Baked cores are hard and strong.
A core is not damaged easily.
Core using oil sand has better collapsable properties.
Dry strength and green strength of the core improve.

Thermoplastic Binders As Core Binders

Common thermoplastic binders used for making cores are as follows

Rosin.
Pitch.
Furan.
Phenol.
Urea.

Thermoplastic binders have the following advantages:

High collapsibility.
Moisture resistance property.
High strength.
Low gas formation.

Core material should be selected properly and characteristics for producing sound core for holes and cavities production.

Sand properties and quality sand testing of sand should be done before using sand and binding material for making the core.

The core material used for making the core should have the same thermal expansion of molten metal.

The difference in thermal expansion of the coefficient of molten metal and material will cause crack defects such as hot tears and warp defects in casting during the solidification process.

Care must be taken to make sure that the thermal expansion of both molten metal and the material used in the core-making is the same.

Core Material In Casting | Core Material In Sand Casting | Mechgrace |